A primary goal of surgical treatment of tumors is the complete removal of abnormal or pathological tissue while sparing normal areas. Hence, a surgeon attempts to distinguish abnormal tissue from adjacent areas of normal tissue and to identify boundaries of pathological tissue so that pathological tissue may be removed without affecting surrounding areas. For example, when removing tumors from the cortex, it is important that substantially all the pathological tissue be removed while minimizing damage to cortical tissue committed to important functions, such as language, motor and sensory areas.
Incidence rates for primary intracranial brain tumors are in the range of 50-150 cases per million population or about 18,000 cases per year. Approximately one half of brain tumors are malignant. Malignant brain tumors in adults occur predominantly in the age range of 40-55 years while the incidence of more benign tumors peaks near 35 years of age. A primary means for treatment of such tumors is surgical removal. Many studies have shown that clinical outcome is improved when more of the total amount of tumor tissue is removed. For gross total resections of tumors, the 5-year survival rate is doubled when compared to subtotal resection. Both duration of survival and independent status of the patient are prolonged when the extent of resection is maximized in malignant gliomas. Current intraoperative techniques do not provide rapid differentiation of tumor tissue from normal brain tissue, especially once the resection of the tumor begins. Development of techniques that enhance the ability to identify tumor tissue intraoperatively may result in maximizing the degree of tumor resection, thereby prolonging survival.
Of the 500,000 patients projected to die of systemic cancer per year in the United States, approximately 25%, or over 125,000, can be expected to have intracranial metastasis. The primary focus for surgery in this group is those patients with single lesions who do not have widespread or progressive cancer. This group represents about 20-25% of patients with metastases (30,000), however, the actual number of patients that are good candidates for surgery is slightly smaller. Currently, of those patients undergoing surgery, one half will have local recurrence of their tumor at the site of operation, while the other half will develop a tumor elsewhere. The fact that about 50% of the surgeries fail at the site of operation means that an improved ability to remove as much tumor as possible by detecting and localizing tumor margins during tumor removal could potentially decrease the incidence of local recurrence.
Thus, for both primary and metastatic tumors, the more tumor tissue removed, the better the outcome and the longer the survival. Further, by maximizing the extent of resection, the length of functional, good quality survival is also increased.
Most current tumor imaging techniques are performed before surgery to provide information about tumor location. Presurgery imaging methods include magnetic resonance imaging (MRI) and computerized tomography (CT). In the operating room, only intraoperative ultrasound and stereotaxic systems can provide information about the location of tumors. Ultrasound shows location of the tumor from the surface, but, once surgery begins, does not provide information to the surgeon necessary to prevent destruction of important functional tissue while permitting maximal removal of tumor tissue. Stereotaxic systems coupled with advanced imaging techniques have (at select few hospitals) been able to localize tumor margins based upon the preoperative CT or MRI scans. However, studies have shown that the actual tumor extends 2-3 cm beyond where the image enhanced putative tumor is located on preoperative images. Therefore, the only reliable method currently available for determining the location of tumors is to obtain multiple biopsies during surgery and wait for results of microscopic examination of frozen sections. This technique, known as multiple histological margin sampling, suffers several drawbacks. First, this is a time-consuming procedure and can add about 30 to 90 minutes (depending upon the number of samples taken) to the length of time the patient is under anesthesia. The increased time required for margin sampling leads to increased medical costs, as operating room time costs are high. Moreover, increased operating room time for the patient increases the probability of infection. Multiple histological margin sampling is prone to errors, as the pathologist must prepare and evaluate samples in short order. In addition, margin sampling does not truly evaluate all regions surrounding a primary tumor and some areas of residual tumor can be missed due to sampling error. Thus, although patient outcome is dependent upon aggressive removal of tumor tissue, a surgeon must often rely upon an estimation technique as a guide. Surgeons must make difficult decisions between aggressively removing tissue and destroying surrounding functional tissue, and may not know the true outcome of the procedure until permanent tissue sections are available about one week later. Consequently, an additional surgical procedure may be required.
Other techniques developed to improve imaging of solid tumor masses during surgery include determining the shape of visible luminescence spectra from normal and cancerous tissue. U.S. Pat. No. 4,930,516 teaches that the shape of visible luminescence spectra from normal and cancerous tissue are different. Specifically, there is a shift to blue with different luminescent intensity peaks in cancerous tissue as compared to normal tissue. Thus it is possible to distinguish cancerous tissue by exciting the tissue with a beam of ultraviolet (UV) light and comparing visible native luminescence emitted from the tissue with luminescence from a non-cancerous control of the same tissue type. Such a procedure is fraught with difficulties since a real time, spatial map of the tumor location is not provided for the use of a surgeon. Moreover, the use of UV light as an excitation wavelength can cause photodynamic changes to normal cells and is dangerous for use in an operating room. In addition, UV light penetrates only superficially into tissue and requires quartz optical components instead of glass.
Optical imaging of tissue using techniques and apparatus similar to those described herein is described in U.S. Pat. Nos. 5,699,798, 5,465,718 and 5,419,989, all of which are incorporated herein by reference in their entirety.
Therefore, there remains a need in the art for a more effective method and device for determining solid tumor locations and precisely mapping tumor margins in a real-time mode during surgery. Such a method and device should further be useful for inexpensive evaluation of any solid tumor by a non-invasive procedure (e.g., breast mammography) and be capable of grading and characterizing tumors.